How much Tzedaka should a non Jew give? Do they also get rewarded?
A Ben-Noach that does a Mitzvah which has a positive effect on himself or on the world around him, like giving Tzedakah, will indeed be rewarded.
However there are no specific Torah guidelines on how much Tzedakah a Ben-Noach should give.
Sources:
רמב״ם הל׳ מלכים פ״י ה״י, רדב״ז שם, וראה בספר ׳שבע מצות השם׳ ח״א פ״ג ה״ו ובהערות שם ובהערה 72.
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